A vehicle navigation device detects a vehicle's current position and travel direction. The vehicle navigation device displays a vehicle mark corresponding to the detection result along with a road map on a display apparatus to provide a driver with vehicle travel guidance.
There is known the vehicle navigation device including a gyro sensor (e.g., see patent literatures 1 and 2). The vehicle navigation device uses known dead-reckoning navigation to detect the vehicle's position and travel direction based on an angular velocity detected by the gyro sensor and a detection signal (vehicle speed or acceleration) from a vehicle speed sensor or an acceleration sensor.
Characteristics of an angular velocity detected by the gyro sensor vary with the ambient environment such as temperature. To solve this issue, the vehicle navigation device including the gyro sensor generally performs zero point correction when the navigation device is started up in response to a power-on or when the vehicle stops from a traveling state (e.g., see patent literature 3). The zero point correction settles a zero point for gyro sensor output.
The zero point correction is performed on the gyro sensor when the vehicle navigation device is started or the vehicle stops travelling. This is because, the vehicle is assumed to be in stationary state in these cases and no angular velocity is applied to the gyro sensor (i.e., angular velocity=0).
After the power is turned on, the gyro sensor requires time to stabilize an output. At startup, the vehicle navigation device performs the zero point correction after an output from the gyro sensor stabilizes.
The zero point correction performed at startup of the vehicle navigation device requires a longer time than the zero point correction performed after the vehicle starts traveling. A driver may start the vehicle before the zero point correction is completed when the zero point correction is performed at the startup of the vehicle navigation device.
The zero point correction is interrupted when the driver starts the vehicle to travel before the normal completion of the zero point correction. In this case, the zero point cannot be settled on the gyro sensor until the next zero point correction. The next zero point correction may be carried out when the vehicle stops after the start of the travelling. Thus, when the zero point correction fails to be normally completed before the start of travelling, the driver is provided with the travel guidance based on incorrect angular velocity information.
The travel guidance displays a road map on the display apparatus. The displayed map contains a vehicle mark that indicates the vehicle's position and travel direction. Occupants of the vehicle may feel uncomfortable due to an abnormal phenomenon such as a straying or drifting vehicle mark.
The vehicle navigation device performs map matching that matches the vehicle position with a road on the road map. When map data does not contain road data corresponding to the vehicle position, a symbol mark is displayed on the display apparatus to notify this situation to the occupant (for example, refer to patent literature 4).
When the zero point correction is not performed on the gyro sensor immediately after the vehicle navigation device starts, the failure of the zero point correction may be displayed on the display apparatus by applying the technology described above. With this configuration, the occupant can be notified of the situation that the vehicle mark displayed on the road map is incorrect.
However, even though the failure of the zero point correction is notified to the occupant, a straying vehicle mark is still displayed on the road map during the travelling. Thus, the proposed technology does not provide a fundamental solution and fails to prevent a user from developing a feeling of distrust.